(rail transport,UK) A small explosive charge (detonator) which can be placed on a railway line in fog, to be detonated by a train passing over it as a warning signal to the driver.
1943 November and December, T. Lovatt Williams, “Some Reminiscences of the Footplate—III”, inRailway Magazine, page344:
The layman does not realise the dreadful nightmare of running in fog, especially at night, when the safety of everyone depends on the driver hearing thefog signal detonate.
1960 November, L. Hyland, “The Irish Scene”, inTrains Illustrated, page691:
The last train—a three-coach A.E.C. unit—from Belfast to Crumlin and back, was bade farewell withfog signals as it carried a capacity crowd of last-trip travellers.
